Effect of L-thyroxine administration on the incidence of iodine induced and spontaneous lymphocytic thyroiditis in the BB/Wor rat.

Chronic L-thyroxine administration (6 micrograms/100g BW, ip, daily) for 2 or 3 months suppressed serum TSH concentrations and decreased both the incidence of spontaneous lymphocytic thyroiditis (LT) and the serum levels of anti-thyroglobulin (anti-Tg) antibodies in the diabetes prone BB/Wor rat. This suggests that TSH may play a role in the occurrence of LT in this rat model. In contrast to these observations, L-thyroxine administration did not affect the markedly increased incidence of LT or the elevated serum anti-Tg antibodies in iodine supplemented BB/Wor rats, suggesting that TSH stimulation is not necessary for the development of iodine induced LT in this rat model. Other factors, such as the increased antigenicity of highly iodinated Tg, may be more important.